Biomethane Production Using Impurity Solidification and CO₂ Separation
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Solution Overview
Problem
Current methods for producing biomethane from biogas struggle with effectively removing impurities like ammonia, volatile organic compounds, water, sulfur, and siloxanes, which limits the biogas' use in natural gas networks due to its high carbon dioxide content and greenhouse gas properties.
Innovation Solution
A three-step process involving drying, partial elimination of impurities through compression and solidification, and separation of methane and carbon dioxide using cyclical sub-stages and scrubbing techniques, with CO2 recycling for efficient impurity removal and regeneration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If biogas is used directly without purification, then it can be used locally for heat and electricity generation, but its high carbon dioxide content reduces calorific value and increases compression and transport costs
Solution Approach 1:
The purification process is divided into three sequential stages: drying to remove water, solidification to remove siloxanes and ammonia, and CO2 separation. This segmentation allows each impurity type to be addressed by a specialized process step, efficiently improving calorific value while maintaining operational feasibility
Solution Approach 2:
The process utilizes parameter changes, particularly temperature and pressure variations, to selectively remove different impurities. Cooling the biogas to below -70°C causes siloxanes and ammonia to solidify, while subsequent CO2 separation further purifies the methane, thereby increasing calorific value
2Adaptability or versatility
If biogas is further purified to natural gas specifications, then it can be injected into natural gas networks and used as biomethane, but multiple treatment steps are required before CO2 separation
Solution Approach 1:
The invention extracts and removes specific impurities (water, siloxanes, ammonia) before the main CO2 separation step. By taking out these interfering substances first, the subsequent CO2 separation process becomes more efficient and the overall purification can achieve natural gas specifications
Solution Approach 2:
The drying and solidification steps are performed as preliminary actions before CO2 separation. This preliminary treatment prevents water and solid impurities from interfering with the CO2 separation process, simplifying the overall system design while achieving the required purification level for network injection
3Manufacturing precision
If impurities are removed by conventional methods, then some purification is achieved, but impurities like siloxanes and ammonia are not effectively eliminated
Solution Approach 1:
The invention exploits phase transitions by cooling the biogas to below -70°C, causing siloxanes and ammonia to transition from gas to solid phase. These solids are then easily separated by filtration or settling, achieving effective removal of these specific impurities that conventional methods miss
Solution Approach 2:
The process replaces conventional mechanical separation methods with a thermal approach using phase transitions. Instead of using complex mechanical separators for siloxanes and ammonia, the invention uses temperature control to naturally precipitate these impurities as solids, simplifying the separation mechanism while improving removal efficiency
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This process enhances biomethane production by removing impurities, improving its calorific value and reducing compression and transport costs, enabling wider use and integration into natural gas networks as a renewable energy source.
Implementation Method 1
a first step of drying the biogas stream
Implementation Method 2
a second step of at least partially eliminating said impurity contained in the dried biogas stream by solidification
Implementation Method 3
a third stage of separating the methane and the carbon dioxide contained in the biogas resulting from the second stage
Data Source
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AI summary
A process for producing biomethane from a biogas stream comprising methane, carbon dioxide and at least one impurity selected from ammonia, volatile organic compounds, water, sulfur impurities (H2S) and siloxanes, comprising: - a first step of drying the biogas stream, - a second step of at least partial removal of said impurity contained in the dried biogas stream by solidification and removal of the impurity; and - a third step of separating the methane and carbon dioxide contained in the biogas from the second step so as to produce a biomethane stream and a CO2 stream.